Which method is best to detect the presence of Pseudomonas aeruginosa in patient samples in the shortest amount of time?
Why is this important?
Pseudomonas aeruginosa is a bacteria that can cause long term infections in patients with CF. It is known that the presence of this bacteria in the lungs is sometimes linked to poorer lung function and quality of life for patients. Once the bacteria is detected, patients usually have intensive antibiotics in an attempt to eradicate the bacteria.
What did you do?
We used existing molecular tests to identify bacteria in samples, as well as designing some new rapid tests. We tried different techniques to extract DNA from respiratory samples, and then tried all the tests to find the best combinations. Our tests will give a positive result if Pseudomonas aeruginosa is present, and tell you if it is the Liverpool Epidemic Strain, the most common transmissible strain in the UK. We trialled these tests on hundreds of samples of sputum, cough swabs and bronchoalveolar lavage fluid (fluid put into a small area of lung via bronchoscopy, and then re-collected for examination). We did this alongside the current diagnostic tests(bacterial cultures), and compared the results to see if we could detect more Pseudomonas positive samples using our rapid methods.
What did you find?
Our methods reduced the time taken for a result by over 24 hours. For adult samples, the new methods were not more sensitive than the methods used now. However, for samples from children, the new methods identified more Pseudomonas positives than the current methods did.
What does this mean and reasons for caution?
The methods appear more sensitive than bacterial culture in children, and could result in Pseudomonas aeruginosa being detected earlier and therefore treated earlier. However, the equipment needed to carry this out is very expensive and may not be available to all diagnostic laboratories. These methods do not give you any indication of other bacteria, viruses or fungi that may be present in the samples and does not give you any information about antibiotic resistance.
These types of rapid methods may be introduced into the diagnostic laboratories but often this takes a very long time and a large investment of money. In the shorter term, this method could be used for samples from children only.